The present invention relates to a yoke component for making up a magnetic circuit of a voice coil motor for a hard disk drive, and a method of deburring the surface of the yoke component, and particularly to a method of deburring a yoke component, which is capable of removing burrs produced on all ridge lines, including ridge lines at finely machined portions, of the yoke component. The present invention also relates to a voice coil motor for a hard disk drive, using the yoke component from which burrs are thus removed.
A voice coil motor for a hard disk drive includes, as shown in FIG. 1, a rare-earth magnet xe2x80x9caxe2x80x9d and a yoke component xe2x80x9cbxe2x80x9d for making up a magnetic circuit of the voice coil motor. In addition, character xe2x80x9ccxe2x80x9d designates a coil. In recent years, along with a tendency to increase the storage capacities of hard disks, flying heights of magnetic heads have come to be reduced, and to prevent occurrence of head crush due to the reductions in flying heights of the magnetic heads, voice coil motors have been increasingly required to be cleaned.
Of components of a voice coil motor, a yoke component manufactured by pressing or cutting has a disadvantage that it has high viscosity causing shearing burrs or cutting burrs. This is because the yoke component is mainly made from a low carbon steel having a high toughness for obtaining an excellent motor performance.
Further, in recent years, since hard disk drives have been miniaturized, yoke components for making up magnetic circuits of voice coil motors used for the hard disk drives have come to be miniaturized and to be complicated in shape. As a result, the number of yoke components having finely machined portions such as through-holes, bends, and threaded holes has been increased, thereby tending to increase the frequency of occurrence of burrs. For example, in a yoke component thus miniaturized and complicated in shape, shearing burrs or cutting burrs of 0.5 mm or less in thickness are often produced in through-holes or threaded holes of about 3 mm in diameter. These burrs adhering on the surface of the yoke component do not necessarily remain adhering thereon but may be easily dropped therefrom due to physical or chemical causes.
Even if burrs are not dropped from the surface of a yoke component, since the surface of the yoke component is subjected to nickel plating, the nickel plating film on the surface may be crushed and a nickel powder be dropped therefrom when an external impact force is applied to the burrs.
The drop of burrs leads to deterioration of the cleanness of a voice coil motor for a hard disk drive, and further causes head crush and the like if the dropped burrs collide with a magnetic head upon operation of the hard disk drive. In particular, since the flying height of a magnetic head has been recently reduced to 0.1 xcexcm or less, the drop of burrs of 0.5 mm or less in thickness has become a cause of head crush.
If a dropped burr adheres on a hard disk, there arises a problem associated with breakage of data recorded in the hard disk because of the ferromagnetic property of the burr. In recent years, since the recording density of a hard disk has become 1 GB/cm2 or more, the drop of a burr of about 0.5 mm in thickness has possibly led to serious breakage of data recorded in the hard disk.
To remove burrs on yoke components for making up magnetic circuits of voice coil motors for hard disk drives, various kinds of deburring methods have been proposed; however, any one of these methods has not succeeded to perfectly remove burrs on yoke components. For example, a deburring method using a barrel polishing treatment is effective to remove large burrs produced on ridge lines around the outer periphery of a yoke component; however, such a method is disadvantageous in that burrs of 0.5 mm or less in thickness present on finely machined portions, such as through-holes, bends, and threaded holes, of the yoke component cannot be removed because abrasive grains do not sufficiently collide therewith.
A burring method using a chemical polishing treatment is effective to remove micro-burrs of 0.1 mm or less in thickness present at any location of a yoke component; however, such a method is disadvantageous in that burrs of more than 0.1 mm and 0.5 mm or less in thickness present on a yoke component cannot be removed by dissolution because of a possibility that longer chemical polishing may dissolve the main body of the yoke component. In general, the chemical polishing treatment is additionally used to make small burrs of 0.5 mm or less present on finely machined portions such as through-holes, bends, or threaded holes, which burrs cannot be removed by barrel polishing because the abrasive grains are larger in size than the finely machined portions, and as described above, the chemical polishing treatment has not effect of perfectly removing such burrs of 0.5 mm or less.
A deburring method using an abrasive grain fluidization treatment is effective to remove whisker-like burrs having fine roots, produced typically upon cutting of a yoke component, by pressing viscoelastic media containing abrasive grains kneaded therein to burrs; however, such a method is disadvantageous in that burrs produced by shearing, which have roots wider than tips, cannot be perfectly removed at the roots. Further, a deburring method using a thermal deburring treatment is disadvantageous in that heat generated at burrs are easy to propagate to the main body of a yoke component, thereby making it difficult to remove the burrs by oxidation; a deburring method using a magnetic polishing treatment is disadvantageous in that even if needle media made from a ferromagnetic material collide with a burr, the burr cannot be removed at the root; and a deburring method using ultrasonic vibration or water pressure is disadvantageous in that burrs produced by shearing cannot be removed at the roots, and therefore, these methods are not generally used for deburring yoke components for making up magnetic circuits of voice coil motors for hard disk drives.
A prior art deburring method has generally used only the barrel polishing treatment or the barrel polishing treatment followed by the chemical polishing treatment to deburr yoke components for making up magnetic circuits of voice coil motors for hard disk drives; however, such a method has failed to remove burrs of 0.5 mm or less in thickness present on finely machined portions, such as through-holes, bends, and threaded holes, of a yoke component, and in some cases, the prior art method has adopted brushing to remove such burrs.
The brushing for finely machined portions on which fine burrs are produced, however, is difficult to be automated because the shapes of yoke components differ for each voice coil motor, and therefore, such brushing must be manually performed, to cause a problem in that the deburring cost is raised.
An object of the present invention is to provide a yoke component for making up a magnetic circuit of a voice coil motor for a hard disk drive, which yoke component has no burr on all ridge lines, particularly, ridge lines at finely machined portions, of the yoke component; to provide a method of deburring a yoke component for making up a magnetic circuit of a voice coil motor for a hard disk drive, which is capable of certainly, efficiently deburring the yoke component; and to provide a voice coil motor for a hard disk drive, using a yoke component from which burrs are thus removed.
The present inventor has made examination to achieve the above object, that is, to certainly, efficiently deburr a yoke component made from a low carbon steel on which burrs are produced upon shearing or cutting work of the yoke component, and found that burrs present on all ridge lines, particularly, ridge lines at finely machined portions (for example, through-holes, threaded holes and recesses, each of which has an diameter of 10 mm or less, and further bends each having a radius of curvature of 5 mm or less) are difficult to be removed only by a barrel polishing treatment because abrasive grains cannot be sufficiently collide with the burrs present on the finely machined portions; however, these burrs present on all ridge lines of the yoke component can be certainly removed by subjecting the yoke component to the barrel polishing treatment, and then subjecting the yoke component to at least one of a thermal deburring treatment, a magnetic polishing treatment, an ultrasonic deburring treatment, and a water jet deburring treatment. The present inventor has thus accomplished the present invention on the basis of the above-described knowledge.
Therefore, according to a first aspect of the present invention, there is provided a yoke component, made from a low carbon steel, for making up a magnetic circuit of a voice coil motor for a hard disk drive, wherein the yoke component has on any ridge line thereof no burr of 0.5 mm or less in thickness.
According to a second aspect of the present invention, there is provided a deburring method of removing burrs present on the surface of a yoke component, made from a low steel carbon steel, of a voice coil motor for a hard disk drive, including: a first step of subjecting the yoke component to a barrel polishing treatment; and a second step of subjecting the yoke component to at least one of an abrasive grain fluidization treatment, a thermal deburring treatment, a magnetic polishing treatment, an ultrasonic deburring treatment, and a water jet deburring treatment.
According to a third aspect of the present invention, there is provided a voice coil motor for a hard disk drive, including: a yoke component, made from a low carbon steel, for making up a magnetic circuit of the voice coil motor, wherein the yoke component has on any ridge line thereof no burr of 0.5 mm or less in thickness.